Spherical objects such as balls present a unique challenge for making a mould. Because the entire surface is curved there is no good point in which you can insert a gap in your mould to pour resin or plaster into. Also, it's very easy for seams to show up. However, you can minimise these risks by making a multi-piece mould. With this, you can fit each piece together to form a rigid whole and pour your casting material in through a small hole at the top.
- Skill level:
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Things you need
- Brown liquid soap
- Modelling clay
- Stirring stick
- Pottery plaster
Lay out newspaper on the floor and place your ball in the middle. Wrap a ¼ inch thick, 1 1/4 inch high ridge of modelling clay around the top of the ball, shaping it into a hollow cone. Place a ¼ inch diameter, 1/12 inch high tower of modelling clay in the middle.
Rub the surface of the ball enclosed in the cone with brown liquid soap. The soap will act as a release, preventing the plaster from sticking too solidly to any surface.
Pour pottery plaster powder into a bucket. Begin to fill it with water, stirring with a stick as you go. When it reaches the consistency of mud, quickly carry it to the ball.
Prop the ball upright with more modelling clay and pour the plaster into the cone. Make sure it is at least an inch thick. Wait an hour and a half for the plaster to harden a bit before flipping the ball over and creating another cone on the opposite side, this time without the modelling clay column in the middle.
Dab soap over the surface of the ball. Mix more plaster up and pour it into the cone. Let it harden for an hour and a half.
Remove the modelling clay from the ball but leave the plaster caps in place. Create a ¼ inch thick, 1 ¼ inch high wall of modelling clay between the two caps on either side of the ball.
Rub soap over both faces of the ball and along the inner edge of both caps. Spread more soap up over the lip of the caps. Mix up more plaster and pour it over one face of the ball. Let it harden for an hour and a half.
Remove the modelling clay and rub the exposed plaster faces with soap. Mix up more plaster and dab it over the last remaining face.
Let the mould sit and harden for a full day.
Remove the four pieces of the mould from your ball. They should not stick together since you coated them with soap. To cast a ball, just fit them together and pour your casting material through the small hole in the top.
Tips and warnings
- Wear a dust mask and gloves when working with the plaster.
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